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<h1 id="firstHeading" class="firstHeading">C 关键词</h1>
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                    <div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr"><div class="t-navbar" style=""><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="../c.html" title="c"> C</a><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="line-height:1.1em;">
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</table></div><div></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><strong class="selflink">C 关键词</strong><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv-col-table"><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/auto.html" title="c/keyword/auto"><span class="t-lines"><span>auto</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/break.html" title="c/keyword/break"><span class="t-lines"><span>break</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/case.html" title="c/keyword/case"><span class="t-lines"><span>case</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/char.html" title="c/keyword/char"><span class="t-lines"><span>char</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/const.html" title="c/keyword/const"><span class="t-lines"><span>const</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/continue.html" title="c/keyword/continue"><span class="t-lines"><span>continue</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/default.html" title="c/keyword/default"><span class="t-lines"><span>default</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/do.html" title="c/keyword/do"><span class="t-lines"><span>do</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/double.html" title="c/keyword/double"><span class="t-lines"><span>double</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/else.html" title="c/keyword/else"><span class="t-lines"><span>else</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/enum.html" title="c/keyword/enum"><span class="t-lines"><span>enum</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/extern.html" title="c/keyword/extern"><span class="t-lines"><span>extern</span></span></a></div></div></td></tr>
</table></div></td><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/float.html" title="c/keyword/float"><span class="t-lines"><span>float</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/for.html" title="c/keyword/for"><span class="t-lines"><span>for</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/goto.html" title="c/keyword/goto"><span class="t-lines"><span>goto</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/if.html" title="c/keyword/if"><span class="t-lines"><span>if</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/inline.html" title="c/keyword/inline"><span class="t-lines"><span>inline</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/int.html" title="c/keyword/int"><span class="t-lines"><span>int</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/long.html" title="c/keyword/long"><span class="t-lines"><span>long</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/register.html" title="c/keyword/register"><span class="t-lines"><span>register</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/restrict.html" title="c/keyword/restrict"><span class="t-lines"><span>restrict</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/return.html" title="c/keyword/return"><span class="t-lines"><span>return</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/short.html" title="c/keyword/short"><span class="t-lines"><span>short</span></span></a></div></div></td></tr>
</table></div></td><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/signed.html" title="c/keyword/signed"><span class="t-lines"><span>signed</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/sizeof.html" title="c/keyword/sizeof"><span class="t-lines"><span>sizeof</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/static.html" title="c/keyword/static"><span class="t-lines"><span>static</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/struct.html" title="c/keyword/struct"><span class="t-lines"><span>struct</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/switch.html" title="c/keyword/switch"><span class="t-lines"><span>switch</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/typedef.html" title="c/keyword/typedef"><span class="t-lines"><span>typedef</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/union.html" title="c/keyword/union"><span class="t-lines"><span>union</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/unsigned.html" title="c/keyword/unsigned"><span class="t-lines"><span>unsigned</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/void.html" title="c/keyword/void"><span class="t-lines"><span>void</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/volatile.html" title="c/keyword/volatile"><span class="t-lines"><span>volatile</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/while.html" title="c/keyword/while"><span class="t-lines"><span>while</span></span></a></div></div></td></tr>
</table></div></td><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/_Alignas.html" title="c/keyword/ Alignas"><span class="t-lines"><span>_Alignas</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/_Alignof.html" title="c/keyword/ Alignof"><span class="t-lines"><span>_Alignof</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/_Atomic.html" title="c/keyword/ Atomic"><span class="t-lines"><span>_Atomic</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/_Bool.html" title="c/keyword/ Bool"><span class="t-lines"><span>_Bool</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/_Complex.html" title="c/keyword/ Complex"><span class="t-lines"><span>_Complex</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/_Generic.html" title="c/keyword/ Generic"><span class="t-lines"><span>_Generic</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/_Imaginary.html" title="c/keyword/ Imaginary"><span class="t-lines"><span>_Imaginary</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/_Noreturn.html" title="c/keyword/ Noreturn"><span class="t-lines"><span>_Noreturn</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/_Static_assert.html" title="c/keyword/ Static assert"><span class="t-lines"><span>_Static_assert</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/_Thread_local.html" title="c/keyword/ Thread local"><span class="t-lines"><span>_Thread_local</span></span></a></div></div></td></tr>
</table></div></td></tr>
<tr class="t-nv-h2"><td colspan="5">预处理器指定</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="preprocessor/impl.html" title="c/preprocessor/impl"><span class="t-lines"><span>_Pragma</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5">条件性支持</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="keyword/fortran.html" title="c/keyword/fortran"><span class="t-lines"><span>fortran</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="https://zh.cppreference.com/mwiki/index.php?title=c/language/asm&amp;action=edit&amp;redlink=1" class="new" title="c/language/asm（页面不存在）"><span class="t-lines"><span>asm</span></span></a></div></div></td></tr>
</table></div><div></div></div></div></div><div class="t-navbar-sep"> </div></div>
<p>这是 C 中保留的关键词列表。因为语言使用这些关键字，故不可重定义它们。 
</p>
<table class="wikitable">

<tr>
<td>
<p><a href="keyword/auto.html" title="c/keyword/auto"><code>auto</code></a><br>
<a href="keyword/break.html" title="c/keyword/break"><code>break</code></a><br>
<a href="keyword/case.html" title="c/keyword/case"><code>case</code></a><br>
<a href="keyword/char.html" title="c/keyword/char"><code>char</code></a><br>
<a href="keyword/const.html" title="c/keyword/const"><code>const</code></a><br>
<a href="keyword/continue.html" title="c/keyword/continue"><code>continue</code></a><br>
<a href="keyword/default.html" title="c/keyword/default"><code>default</code></a><br>
<a href="keyword/do.html" title="c/keyword/do"><code>do</code></a><br>
<a href="keyword/double.html" title="c/keyword/double"><code>double</code></a><br>
<a href="keyword/else.html" title="c/keyword/else"><code>else</code></a><br>
<a href="keyword/enum.html" title="c/keyword/enum"><code>enum</code></a><br>
<a href="keyword/extern.html" title="c/keyword/extern"><code>extern</code></a>
</p>
</td>
<td>
<p><a href="keyword/float.html" title="c/keyword/float"><code>float</code></a><br>
<a href="keyword/for.html" title="c/keyword/for"><code>for</code></a><br>
<a href="keyword/goto.html" title="c/keyword/goto"><code>goto</code></a><br>
<a href="keyword/if.html" title="c/keyword/if"><code>if</code></a><br>
<a href="keyword/inline.html" title="c/keyword/inline"><code>inline</code></a> <span class="t-mark-rev t-since-c99">(C99 起)</span><br>
<a href="keyword/int.html" title="c/keyword/int"><code>int</code></a><br>
<a href="keyword/long.html" title="c/keyword/long"><code>long</code></a><br>
<a href="keyword/register.html" title="c/keyword/register"><code>register</code></a><br>
<a href="keyword/restrict.html" title="c/keyword/restrict"><code>restrict</code></a> <span class="t-mark-rev t-since-c99">(C99 起)</span><br>
<a href="keyword/return.html" title="c/keyword/return"><code>return</code></a><br>
<a href="keyword/short.html" title="c/keyword/short"><code>short</code></a>
</p>
</td>
<td>
<p><a href="keyword/signed.html" title="c/keyword/signed"><code>signed</code></a><br>
<a href="keyword/sizeof.html" title="c/keyword/sizeof"><code>sizeof</code></a><br>
<a href="keyword/static.html" title="c/keyword/static"><code>static</code></a><br>
<a href="keyword/struct.html" title="c/keyword/struct"><code>struct</code></a><br>
<a href="keyword/switch.html" title="c/keyword/switch"><code>switch</code></a><br>
<a href="keyword/typedef.html" title="c/keyword/typedef"><code>typedef</code></a><br>
<a href="keyword/union.html" title="c/keyword/union"><code>union</code></a><br>
<a href="keyword/unsigned.html" title="c/keyword/unsigned"><code>unsigned</code></a><br>
<a href="keyword/void.html" title="c/keyword/void"><code>void</code></a><br>
<a href="keyword/volatile.html" title="c/keyword/volatile"><code>volatile</code></a><br>
<a href="keyword/while.html" title="c/keyword/while"><code>while</code></a>
</p>
</td>
<td>
<p><a href="keyword/_Alignas.html" title="c/keyword/ Alignas"><code>_Alignas</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span><br>
<a href="keyword/_Alignof.html" title="c/keyword/ Alignof"><code>_Alignof</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span><br>
<a href="keyword/_Atomic.html" title="c/keyword/ Atomic"><code>_Atomic</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span><br>
<a href="keyword/_Bool.html" title="c/keyword/ Bool"><code>_Bool</code></a> <span class="t-mark-rev t-since-c99">(C99 起)</span><br>
<a href="keyword/_Complex.html" title="c/keyword/ Complex"><code>_Complex</code></a> <span class="t-mark-rev t-since-c99">(C99 起)</span><br>
<a href="keyword/_Generic.html" title="c/keyword/ Generic"><code>_Generic</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span><br>
<a href="keyword/_Imaginary.html" title="c/keyword/ Imaginary"><code>_Imaginary</code></a> <span class="t-mark-rev t-since-c99">(C99 起)</span><br>
<a href="keyword/_Noreturn.html" title="c/keyword/ Noreturn"><code>_Noreturn</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span><br>
<a href="keyword/_Static_assert.html" title="c/keyword/ Static assert"><code>_Static_assert</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span><br>
<a href="keyword/_Thread_local.html" title="c/keyword/ Thread local"><code>_Thread_local</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span>
</p>
</td></tr></table>
<p>最常见的以下划线开头的关键词通常通过其便利宏来使用：
</p>
<table class="wikitable">

<tr>
<td>关键词
</td>
<td>用作
</td>
<td>定义于
</td></tr>
<tr>
<td><a href="keyword/_Alignas.html" title="c/keyword/ Alignas"><code>_Alignas</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span>
</td>
<td><a href="types.html" title="c/types"><tt>alignas</tt></a>
</td>
<td><code>stdalign.h</code>
</td></tr>
<tr>
<td><a href="keyword/_Alignof.html" title="c/keyword/ Alignof"><code>_Alignof</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span>
</td>
<td><a href="types.html" title="c/types"><tt>alignof</tt></a>
</td>
<td><code>stdalign.h</code>
</td></tr>
<tr>
<td><a href="keyword/_Atomic.html" title="c/keyword/ Atomic"><code>_Atomic</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span>
</td>
<td><a href="atomic.html" title="c/atomic"><tt>atomic_bool. atomic_int, ...</tt></a>
</td>
<td><code>stdatomic.h</code>
</td></tr>
<tr>
<td><a href="keyword/_Bool.html" title="c/keyword/ Bool"><code>_Bool</code></a> <span class="t-mark-rev t-since-c99">(C99 起)</span>
</td>
<td><a href="types/boolean.html" title="c/types/boolean"><tt>bool</tt></a>
</td>
<td><code>stdbool.h</code>
</td></tr>
<tr>
<td><a href="keyword/_Complex.html" title="c/keyword/ Complex"><code>_Complex</code></a> <span class="t-mark-rev t-since-c99">(C99 起)</span>
</td>
<td><a href="numeric/complex/complex.html" title="c/numeric/complex/complex"><tt>complex</tt></a>
</td>
<td><code>complex.h</code>
</td></tr>
<tr>
<td><a href="keyword/_Generic.html" title="c/keyword/ Generic"><code>_Generic</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span>
</td>
<td>（无宏）
</td>
<td>
</td></tr>
<tr>
<td><a href="keyword/_Imaginary.html" title="c/keyword/ Imaginary"><code>_Imaginary</code></a> <span class="t-mark-rev t-since-c99">(C99 起)</span>
</td>
<td><a href="numeric/complex/imaginary.html" title="c/numeric/complex/imaginary"><tt>imaginary</tt></a>
</td>
<td><code>complex.h</code>
</td></tr>
<tr>
<td><a href="keyword/_Noreturn.html" title="c/keyword/ Noreturn"><code>_Noreturn</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span>
</td>
<td><a href="types.html" title="c/types"><tt>noreturn</tt></a>
</td>
<td><code>stdnoreturn.h</code>
</td></tr>
<tr>
<td><a href="keyword/_Static_assert.html" title="c/keyword/ Static assert"><code>_Static_assert</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span>
</td>
<td><a href="error/static_assert.html" title="c/error/static assert"><tt>static_assert</tt></a>
</td>
<td><code>assert.h</code>
</td></tr>
<tr>
<td><a href="keyword/_Thread_local.html" title="c/keyword/ Thread local"><code>_Thread_local</code></a> <span class="t-mark-rev t-since-c11">(C11 起)</span>
</td>
<td><a href="thread/thread_local.html" title="c/thread/thread local"><tt>thread_local</tt></a>
</td>
<td><code>threads.h</code>
</td></tr></table>
<p>而且，每个以双下划线 __ 或单下划线跟随大写字母为首的名称是受保留的：细节参阅<a href="language/identifier.html#Reserved_identifiers" title="c/language/identifier">标识符</a>。
</p><p>注意合字符 <code>&lt;%</code> 、 <code>%&gt;</code> 、 <code>&lt;:</code> 、 <code>:&gt;</code> 、 <code>%:</code> 以及 <code>%:%:</code> 提供<a href="language/operator_alternative.html" title="c/language/operator alternative">表示标准记号的替用方式</a>。
</p><p>下列记号在用于<a href="preprocessor.html" title="c/preprocessor">预处理器</a>指令语境<i>之内</i>时，为预处理器所识别：
</p>
<table class="wikitable">

<tr>
<td>
<p><a href="preprocessor/conditional.html" title="c/preprocessor/conditional"><tt>if</tt></a><br>
<a href="preprocessor/conditional.html" title="c/preprocessor/conditional"><tt>elif</tt></a><br>
<a href="preprocessor/conditional.html" title="c/preprocessor/conditional"><tt>else</tt></a><br>
<a href="preprocessor/conditional.html" title="c/preprocessor/conditional"><tt>endif</tt></a><br>
<a href="preprocessor/conditional.html" title="c/preprocessor/conditional"><tt>defined</tt></a>
</p>
</td>
<td>
<p><a href="preprocessor/conditional.html" title="c/preprocessor/conditional"><tt>ifdef</tt></a><br>
<a href="preprocessor/conditional.html" title="c/preprocessor/conditional"><tt>ifndef</tt></a><br>
<a href="preprocessor/replace.html" title="c/preprocessor/replace"><tt>define</tt></a><br>
<a href="preprocessor/replace.html" title="c/preprocessor/replace"><tt>undef</tt></a><br>
</p>
</td>
<td>
<p><a href="preprocessor/include.html" title="c/preprocessor/include"><tt>include</tt></a><br>
<a href="preprocessor/line.html" title="c/preprocessor/line"><tt>line</tt></a><br>
<a href="preprocessor/error.html" title="c/preprocessor/error"><tt>error</tt></a><br>
<a href="preprocessor/impl.html" title="c/preprocessor/impl"><tt>pragma</tt></a><br>
</p>
</td></tr></table>
<p>下列记号用于预处理器指令的语境<i>之外</i>时，为预处理器所识别：
</p>
<table class="wikitable">

<tr>
<td>
<p><a href="preprocessor/impl.html" title="c/preprocessor/impl"><tt>_Pragma</tt></a><span class="t-mark-rev t-since-c99">(C99 起)</span>
</p>
</td></tr></table>
<p>下列的额外关键词被分类为扩展，而且为条件性支持：
</p>
<table class="wikitable">

<tr>
<td>
<p><a href="https://zh.cppreference.com/mwiki/index.php?title=c/language/asm&amp;action=edit&amp;redlink=1" class="new" title="c/language/asm（页面不存在）"><tt>asm</tt></a><br>
<a href="keyword/fortran.html" title="c/keyword/fortran"><code>fortran</code></a>
</p>
</td></tr></table>
<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
<div class="t-ref-std-11">
<ul><li> C11 standard (ISO/IEC 9899:2011): 
</li></ul>
<dl><dd><ul><li> 6.4.1 Keywords (p: 58-59)
</li></ul>
</dd></dl>
<dl><dd><ul><li> J.5 Common extensions (p: 579-581)
</li></ul>
</dd></dl>
<div class="t-ref-std-c99">
<ul><li> C99 standard (ISO/IEC 9899:1999): 
</li></ul>
<dl><dd><ul><li> 6.4.1 Keywords (p: 50)
</li></ul>
</dd></dl>
<dl><dd><ul><li> J.5 Common extensions (p: 511-513)
</li></ul>
</dd></dl>
<div class="t-ref-std-c89">
<ul><li> C89/C90 standard (ISO/IEC 9899:1990): 
</li></ul>
<dl><dd><ul><li> 3.1.1 Keywords 
</li></ul>
</dd></dl>
<dl><dd><ul><li> G.5 Common extensions 
</li></ul>
</dd></dl>
</div>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<table class="t-dsc-begin">

</table></div>
</div>

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